1. Field of the Invention
The present invention relates to an element and a photovoltaic cell.
2. Background of the Invention
Generally, a surface electrode is provided on a silicon photovoltaic cell. The wiring resistance or the contact resistance of the surface electrode relates to a voltage loss that is relevant to conversion efficiency. In addition, the width or the shape of the surface electrode affects the amount of incident sunlight.
The surface electrode of a photovoltaic cell is typically formed in the following manner. Specifically, a conductive composition is applied onto an n-type semiconductor layer that is formed by thermally diffusing phosphorus or the like into the light-receiving side of a p-type semiconductor substrate at high temperature, and a surface electrode is formed by sintering the applied conductive composition at from 800° C. to 900° C. The conductive composition for forming the surface electrode includes a conductive metal powder, glass particles, additives of various kinds and the like.
As the conductive metal powder, a silver powder is generally used. However, use of a powder of metal other than silver has been considered for various reasons. For example, a conductive composition that can form an electrode for a photovoltaic cell that includes silver and aluminum has been disclosed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2006-313744).
Further, a composition for forming an electrode that includes metal nanoparticles that include silver and particles of metal other than silver has been disclosed (see, for example, JP-A No. 2008-226816).
Silver, which is typically used for forming an electrode, is a noble metal whose resource is limited and the price of a bare metal is high. Therefore, proposal of alternative materials for a silver-containing conductive composition (silver-containing paste) has been expected. Copper, which is used for semiconductor wiring materials, is a prospective material that will replace silver. Copper is abundant in supply and the price of a bare metal is about a hundredth of the price of silver.
However, copper is easily oxidized at high temperature of 200° C. or more. Accordingly, for example, in a case of forming an electrode from the composition described in JP-A 2006-313744 that includes copper as a conductive metal, a special process of sintering the composition in an atmosphere of nitrogen or the like is required.
The present invention aims to provide an element having an electrode in which oxidation of copper during sintering is suppressed and the resistivity is lowered, and a photovoltaic cell having the element.